Mass spectrometer



Oct. 5, 1943- J. A. HIPPLE, JR

MASS SPECTROMETER Filed Aug. 2, 1940 INVENTOR ATT NEY l l lll l lll WITNESSES:

Patented Oct. 5, 1943 MASS SPECTROMETER.

John A.'Hipple, Jr., Forest Hills, Pa.,

assig-nor to Westinghouse Electric & Manufacturing'Company, East Pittsburgh, Pa.,

Pennsylvania a corporation of Application August 2, 1940, Serial No. 349,395

9 Claims.

The present invention relates to a device for analyzing the composition of matter and it has particular relation to an arrangement wherein a mass spectrograph is employed to continuously analyze a gas for a plurality of different constituents.

The mass spectrograph, or mass spectrometer as it is also known, is widely used for separating particles having a particular mass or atomic weight from a gaseous composition. There are many types of this instrument a number of which are described along with the principles of operation in an article by Walker Bleakney, entitled "The Mass Spectrograph and Its Uses published on pages 12 to 23, inclusive of the February 1936 issue of "The American Physics Teacher. Briefly stated, the mass spectrometer ionizes the particles of material to be analyzed and subjects them to the action of a combination of electrostatic or magnetic fields or both to cause only those particles having a particular ratio of mass to electric charge to impinge on a current collecting member. The current received by the collector may then be amplified and measured by means of a galvanometer or like device. Since it is possible, by adjusting the ionizing potential to a relatively low value, to prevent any substantial number of particles from receiving a multiple charge, the device may be made to efiectively segregate particles according to the mass alone instead of the ratio m/e where m is the mass or atomic weight of the particle. and e is its charge.

The mass spectrometer,. in many cases, offers advantages over chemical methods of analyzing material and is thus suitable for a number of applications such, for example, as the analysis of soil gas for petroleum prospecting as suggested in U. S. Patent No. 2,112,845 to Howell. For this purpose, as well as for analyzing annealing furnace gases and other uses, it is desirable to provide an arrangement which will iumish a substantially continuous analysis of the gas for a plurality of different constituents thereof. As an example, in the case of furnace gases, it may be required that the carbon, moisture, nitrogen and carbon monoxide content be kept within predetermined limits.

According to the present invention, the focusing characteristics of a mass spectrometer are periodically changed through a predetermined cycle so as to focus particles of each of the plurality of masses which it is desired to measure, on a current collector during a portion of each period. The current through the collector may film recording system be measured continuously to indicate or record its magnitude and a code arrangement may be provided to distinguish between the various masses. In this manner, a single spectrometer of a usual type provides what is in effect a continuous indication of the amount of each of a plurality of materials or elements in a sample of a gas subject to change in composition.

It is, accordingly, an object of the present invention to provide a novel and improved device for analyzing the composition of matter.

Another object of the invention is to provide a novel device for continuously analyzing a gas which is subject to change in composition for a plurality of different constituents.

A further object of the invention is to provide an arrangement wherein a single mass spectrometer will furnish what is in effect a continuous analysis of a gas for a plurality of different constituents.

Other objects and advantages of the invention will appear from the following detailed description taken in conjunction with the accompanying drawing in which,

' Figure 1 is a schematic diagram, with parts in horizontal section, of apparatus embodying the present invention,

Fig. 2 is a vertical sectional of the apparatus of Fig. 1,

Fig. 3 is a. view of a photographic record such as might be produced by the apparatus of Fig. 1, and

Fig. 4 is a schematic view of an indicator arrangement which may be used in lieu of the of Fig. 1.

Referring to the drawing, the apparatus includes a glass tube or vessel 2, which is approximately semi-circular in shape and may be of round cross-section, disposed within an electro magnet 4. The interior of the vessel 2 is provided with a grounded metallic lining or coating 5 in a usual manner. The magnet 4 is energized to provide a uniform magnetic field throughout its interior with its lines of force perpendicular to the plane of the tube and may be of the type described in my copending U. S. patent application Serial No. 296,607 filed September 26, 1939 which has matured into Patent Number 2,265,041. A chamber 6 which may be an annealing furnace communicates by means of a tube or pipe 8 with the interior of the vessel 2' through an opening ill at anend thereof. The tube 8 may include a capillary for allowing a small continuous sample of the atmosphere in view of a portion the chamber 6 to enter the tube which is evacuated through a pump l2.

Within the tube 2 at the end which communicates with the vessel 6 is a filament or cathode -|4 disposed immediately above a slot |6 in a right angled shield l8 which defines an ionizing chamber at 20. A conducting plate 2| is located at the bottom of the chamber as shown to neutralize excess electrons. Disposed wJ-hin the tube 2 immediately in front of the ionizing chamber are a. pair of ion accelerating plates 22 and 24 having aligned narrow vertical slots at 25 and 26 respectively. In the other end of the vessel is a baflle plate 28 having a narrow slot at 30. It will be noted that the center line A of the 'tube between the slot 26 in plate 24 and slot 30 I minals and the shield |8 to maintain the latter member at a positive potential with respect to the filament. The accelerating plate 22 is maintained at a potential intermediate that of the filament and the shield H! by means of a conductor 36 extending from an intermediate point on a resistor 38 connected in shunt with the battery 34. A conductor 40 electrically connects the plate 24 to the negative terminal of a relatively high voltage battery 42 which is grounded as indicated at 44 and shunted by a potentiometer or resistor 46 having difierent potential taps at 48, 58 and 52.

The metallic coating 5 on the interior of the vessel 2 is connected to ground as indicated at 1 so that any ions falling thereon are neutralized in a usual manner.

The plate 28 is also grounded as indicated at 3| so that no electric field will act on the particles after they have entered the analyzer proper between it and the accelerating plate 24.

'A periodic switch indicated generally at 54 includes a stationary plate 56 with perimetral conductor segments 49, 5| and 53 connected to taps 48, 50 and 52 respectively. In addition, the plate 56 includes a circular conducting portion 58 which is connected by a conductor 60 to the positive end of the resistor 38. A conducting arm 62 is arranged to be rotated about the center of the switch plate by means of a motor designated as 64 to periodically connect the conducting terminal 58 with each of the segments 49, 5| and 53.

Located in back of the baffle plate 28 in line with the slot 30 is a current collector 66 which is preferably a plate of conducting metal. The

'collector 66 is connected through a conductor 68 to an amplifier 10 which is grounded at 12 while the output of the amplifier is impressed on a galvanometer 14 by conductors 16. A mirror or reflector 18 is attached to the moving coil of the galvanometer to reflect a light beam from a lamp 80 along a slot 82 in a hood member 84 in proportion to its energization. The slotted hood 84 is provided to prevent the length of the reflectedlight beam, which is generally in the form of a line rather than a point which is most desirable, from producing an indistinct record on a photographic film 86. The film 86 is wound on rollers 88 which are mechanically connected by a belt 90 and may be driven by the switch motor 64.

With the evacuating pump l2 in operation and masses to their electric charges or m/e.

a continuous sample of the gas in the chamber 6 passing into the vessel through the opening ID, the operation of the device is as follows: Electrons from the filament or cathode 4, with the aid of the shield |8 which is at a positive potential withrespect thereto pass through the opening l6 and impinge on the gas in the chamber 20 to ionize the particles. The positive ions are attracted toward the plate 22 and are accelerated by the electric field between the plates 22 and 24 to a uniform energy. Ions of the same mass directed in the straight line with the slots 25 and 26, pass therethrough with equal velocities into the circular portion of the tube provided they are singly charged. The ions passing along this'straight line will include particles having masses of all the difierent atomic weights constituting the gas sample and will then be deflected by the magnetic field from the magnet 4 in proportion to the ratio of their respective Thus for a particular accelerating voltage and assuming the charges e of the different particles are equal, particles of a particular mass will follow the path indicated at a and pass through the opening 30 in plate 28 to fall on the collector 65. In the apparatus shown, the radius of curvature of the path of the ions in the curved portion of the tube is equal to I m V it ra) where V represents the accelerating voltage between the plates 22 and 24 and H the strength of the magnetic field employed. It will be evident from the equation that the above described relationship exists.

With the switch arm 62 engaging segment 49 as shown in the drawing, the accelerating voltage between the plates 22 and 24 isdetermined by the voltage between tap 48 and ground 44 and a particular mass A, which may be carbon dioxide having an atomic weight of 44, will be focused on the collector 66. Since the film 86 is moving along with the switch arm, the image made thereon during this time will be as shown at A on Fig. 3 which represents the film 86 with the time axis horizontal and the ion current axis vertical. With the switch arm moving in a clockwise direction, there will be no voltage across the accelerating plates and consequently no ion current when it is between the segments 49 and 5|. When the arm contacts the segment 5 I however, a voltage determined by the location of the tap 50 is impressed across the accelerating plates to focus upon the collector particles of mass B, which, for example, may be nitrogen having an atomic weight of 18. Since the switch segment 5| is shorter than the segment 49, the indication B on the film in Fig. 3 will be correspondingly shorter than that at A. In a similar manner, the tap 52 is arranged so that with the switch arm at 53, the voltage across the accelerating plates is such as to focus particles of mass C, which may be carbon with an atomic weight of 12, on the collector to produce the indication shown at C in Fig. 3.

Because of the sampling arrangement employed, the number of ions of each mass within the ionizing chamber 20 at any time is propor tional to the amount of the corresponding constituent in the atmosphere of the gas chamber. The number of ions engaging the collector and consequently the current therethrQugh are in turn, proportional to the number of ions of the focused mass in the chamber 20, with the result that the plate current is proportional to the amount of that constituent in the main chamber 6. If desired, the recorded value of the ion current may be operated on by a factor determined by the size of the sample to obtain the percentage of that constituent in the atmosphere in question.

It is preferred to make the switch segment 49 of greater length than segments and 53 in order that the different masses may be readily identified upon the photographic record. Thus the indication of mass A may be identified at I any point in Fig. 3 because of the length of indication and since the sequence in which the masses are focused on the collector is known, any other mass may be identified with respect thereto. If desired, the code arrangement may be omitted and synchronized movement of the switch arm and film utilized for identification.

In Fig. 4 is shown a device which may be employed in place of the photographic arrange ment for indicating rather than recording the 7 results of the analysis. A disc 92 having colored filter segments 49a, 5| a and 53a is disposed be tween the lamp 80 and the galvanometer mirror 18. The segments 49a, 5la and 53a which are preferably of different colors and correspond with the segments 49, 5| and 53 while the disc itself may be mounted on a shaft 94 which is driven by the switch motor 64. The mirror 18 thus reflects a light beam along a scale 95 in proportion to the ion current and this beam is of a color corresponding to the mass being measured at the particular time.

If desired the result of the analysis may be recorded by means of a standard commercial device using increased amplification or some other suitable pen recorder arrangement instead of the photographic device shown in Fig. 1.

From the foregoing description, it will appear that the present invention provides a convenient and relatively inexpensive means for analyzing a continuous gas sample for a plurality of constituents having different masses, respectively. Although the device provides a series of interrupted indications or recordings and is thus not strictly continuous for, all practical purposes its results are as useful as a completely continuous indication would be. The apparatus may be employed to indicate the composition of a gas in an annealing furnace, for example, and manual adjustments may be made to maintain the percentage of the constituents within the desired limits. If preferred the arrangement may be connected with suitable automatic controls for accomplishing these same results.

While the invention has been described with reference to a particular embodiment thereof, it will be evident that various modifications may be made therein without departing from its spirit andscope.

I claim as my invention:

1. A device for continuously analyzing a gaseous atmosphere subject to change in composition comprising means for supplying a continuous sample of said atmosphere, means for ionizing particles of said sample, a current collector, means adjustable to selectively focus ionized particles of each of a plurality of predetermined masses on said current collector, means for continuously controlling the adjustment of said focusing means to individually focus each of said predetermined masses on said current collector periodically and respectively in a predetermined sequence, and means for measuring the ion current received by said current collector.

2. A device for continuously analyzing a gaseous atmosphere subject to change in composition comprising means for supplying a continuous sample of said atmosphere, means for ionizing particles of said sample, a current collector, means adjustable to a plurality of different predetermined conditions to selectively focus ionized particles of each of a plurality of predetermined masses on said current collector, means including a driving motor for continuously controlling the adjustment of said focusing means to periodically change it from one to another of said plurality of predetermined conditions in a predetermined sequence, said last-named means cooperating with said focusing means to maintain it in one of said predetermined conditions for a longer portion of each adjustment period than it is maintained in a different one of said conditions, and means for measuring the ion current received by said current collector.

3. A device for continuously analyzing a gaseous atmosphere subject to change in composition comprising means for supplying a continuous sample of said atmosphere, means for ionizing particles of said sample, a current collector, means adjustable to a plurality of different predetermined conditions to selectively focus ionized particles of each of a plurality of predetermined masses on said current collector, means including a motive device for continuously controlling the adjustment of said focusing means to periodically change it from one to another of said plurality of predetermined conditions in a predetermined sequence, said last-named means cooperating with said focusing means to maintain it in one of said predetermined conditions for a longer time in each period of adjustmentthan it is maintained in a different one of said conditions, and means driven in synchronism with said motive device for recording the instantaneous value of the ion current received by said current collector.

4. A device for continuously analyzing a gaseous atmosphere for a plurality of constituents comprising means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample, a current collector, means operable in response to an electric potential impressed across a control means included therein to focus on said current collector the ionized particles of said sample having a mass to charge ratio determined by the magnitude of said impressed potential, a potential source having terminals adapted to provide a plurality of different predetermined potentials each of which is of such a magnitude as to cause ionized particles of a mass to charge ratio corresponding to a different one of said constituents to be focused on said collector, means for periodically impressing on said control means each of said predetermined potentials in a predetermined sequence, and means for measuring the ion current received by said current collector.

5. In mass spectrograph equipment for continuously analyzing a gaseous atmosphere for a plurality of constituents, means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample, a current collector, means operable in response to an electric potential impressed across a control means included therein to focus onsaid current collector the ionized particles of said sample having a mass determined by the magnitude of said impressed potential, a'potential source having terminals adapted to provide a plurality of different predetermined potentials each of which is of such a magnitude as to cause ionized particles of a different one of said constituents to be focused on said current collector when impressed on said control means, means including a driving motor operable at a substantially uniform speed to impress on said control means each of said predetermined potentials in a predetermined sequence in a uniform periodic manner, and means for measuring the ion current received by said current collector.

6. In mass spectrograph equipment for continuously analyzing a gaseous atmosphere for a plurality of constituents, means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample so that substantially all the ionized particles have the same charge, a current collector, means operable in response to a unidirectional potential impressed across a control means included therein to focus on said current collector the ionized particles of said sample having a mass determined by the magnitude of said potential, a potential source having terminals adapted to provide a plurality of diiferent predetermined potentials each of which is of such a magnitude as to cause ionized particles of a different one of said constituents to be focused on said current collector when impressed on said control means, a switch connected to said potential source and movable to each of a plurality of positions to selectively energize said control means with each of said predetermined potentials, means fordriving said switch at a substantially uniform rate to periodically impress each of said predetermined potentials on said control means in a predetermined sequence, and means for measuring the ion current received by said current collector.

7. In mass spectrograph equipment for continuously analyzing a gaseous atmosphere for a plurality of constituents, means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample so that substantially all the ionized particles have the same charge, a current collector, means operable in response to a unidirectional potential impressed across a control means included therein to focus on said current collector the ionized particles of said sample having a mass determined by the magnitude of said potential, a potential source having terminals adapted to provide a plurality of different predetermined potentials each of I tials on said control means in a predetermined sequence, said switch being such that one of said predetermined potentials is maintained across said control means for a longer portion of each period than is another of said predetermined potentials, and means for measuring the ion current received by said current collector.

8. In mass spectrograph equipment for continuously analyzing a gaseous atmosphere for a plurality of constituents, means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample, a current collector, means operable inresponse to a unidirectional potential impressed across a control means included therein to focus on said current collector.

the ionized particles of said sample having a particular mass determined by the magnitude of said potential, apotential source having terminals adapted to provide a. plurality of different predetermined potentials each of which is of such a magnitude as to cause ionized particles of a different one of said constituents to be focused on said current collector, means including a motive device for connecting the terminals of said potential source supplying each of said predetermined potentials in a predetermined sequence across said control means in a uniform periodic manner, means for continuously indicating the amount of ion current engaging said current collector, and means synchronized with said connecting means for characterizing the indication of said last-named means with a quality depending upon which of said constituents is being measured at any instant.

9. In mass spectrograph equipment for continuously analyzing a gaseous atmosphere for a plurality of constituents, means for obtaining a continuous sample of said atmosphere, means for ionizing particles in said sample so that substantially all the ionized particles have the same charge, a current collector, means operable in response to a unidirectional potential impressed across a control means included therein to focus on said current collector the ionized particles of said sample having a particular mass determined by the magnitude of said potential, a potential source having terminals adapted to provide a plurality of different predetermined potentials each of which is of such a magnitude as to cause ionized particles of a different one of said constituents to be focused on said current collector, means including a motive device for connecting the terminals of said potential source supplying each of said predetermined potentials in a predetermined sequence across said control means in a uniform periodic manner, said last-named means being adapted to maintain one of said predetermined potentials on said control means for a different portion of each period than it maintains a difierent one of said predetermined potentials thereacross, and a device including a member movable at a uniform rate for providing a record of the ion current on said current collector with respect to time.

JOHN A. HIPPLE, JR. 

